Update toolbar's download button style

[simonhong]

In progress (captured from figma)

Completed

[kjozwiak]

The above requires 1.50.110 or higher for 1.50.x verification 👍

[kjozwiak]

@rebron maybe we should look into using another colour for the progress indication in dark mode? It's pretty hard to see as we're using a dark blue against black. It's not the easiest to see. Example via brave/brave-core#17769 (comment).

[rebron]

@aguscruiz We probably want to go lighter color for contrast for dark mode. Really subtle with the progress bar.

[LaurenWags]

Verified with

Brave | 1.50.110 Chromium: 112.0.5615.49 (Official Build) (x86_64)
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Revision | bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS | macOS Version 12.6.4 (Build 21G526)

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Verification PASSED on

Brave	1.50.108 Chromium: 112.0.5615.39 (Official Build) (64-bit) 
Revision	a0e7b9718a92bcd1cf33b7c95316caff3fc20714-refs/branch-heads/5615@{#753}
OS	Linux

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[MadhaviSeelam]

Verification PASSED

Brave | 1.50.110 Chromium: 112.0.5615.49 (Official Build) (64-bit)
-- | --
Revision | bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS | Windows 11 Version 22H2 (Build 22621.1413)

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download in-progress	download complete

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download in-progress	download complete

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download in-progress	download complete